As a coil to be used in a rotary electric machine, there is a wound coil made of a flat wire having a rectangular cross section besides a wound coil made of a wire having a circular cross section. To increase an amount of electric current allowed to flow in the coil, the coil must be formed of a thick wire. Such increase in cross sectional area of the wire tends to deteriorate a space factor of the wound coil made of the circular cross-section wire. On the other hand, the wound coil made of the rectangular cross-section wire is less likely to deteriorate a space factor even when the wire has a larger cross sectional area.
The coil for use in the rotary electric machine to be mounted in a vehicle is heretofore required to be compact and have high performance. In particular, the rotary electric machine used in a vehicle driving section has to be supplied with a large amount of current, whereas the rotary electric machine has a severe limitation in size because it needs to be installed in an engine room. Accordingly, the coil made of the flat wire having a rectangular cross section capable of enhancing the space factor is preferably used in a vehicle-mounted drive motor.
However, such rotary electric machine needs a coil of a non-circular outer shape, more preferably, of an outer shape as near as possible to a rectangular shape in order to shorten the length of a coil end. Such non-circular coil is likely to cause various problems in a manufacturing process due to a difference in winding speed between a long side portion and a short side portion. If winding is done at an extreme low speed, even a non-circular coil could be wound easily. However, for enhancing productivity, the non-circular coil must be wound at high speed.
JP2002-184639A discloses a technique for producing a coil from such a flat wire. This technique winds the flat wire on an elliptic cylindrical winding core by rotating the core. The flat wire is thus wound on the winding core to follow the shape of the winding core. Furthermore, the flat wire is pressed by a retaining member against a fixing member that rotates together with the winding core to restrain expansion of the flat wire and vibration or wobble of the wire during winding.
This retaining member is slidable in a thickness direction of a coil to be produced. As the winding of the flat wire is advanced, the retaining member will move apart from the fixing member. A brake means is provided at a predetermined position perpendicular to the winding core to cause resistance in movement of the flat wire. This brake means is movable together with the retaining member in an axis direction of, the winding core.
The flat wire is wound as pressed by the retaining member in such a way. Accordingly, during winding of the flat wire on the elliptic cylindrical winding core, it is possible to prevent inertia vibration or wobble of the flat wire due to a difference in winding speed in a long side portion and a short side portion, and hence achieve high speed coil winding.
JP2006-288025A discloses a technique related to a rectangular coil, a rectangular coil manufacturing method, and a rectangular coil manufacturing apparatus. A bending device for edgewise bending a rectangular flat wire includes holding means for clamping a linear flat wire, the holding means having a groove equal in width to the flat wire, roller-shaped restriction means which will come into contact with an inner periphery of the flat wire during edgewise bending, and pressing means which will come into contact with an outer periphery of the flat wire during the edgewise bending and rotate to edgewise bend the flat wire.
The flat wire is passed through the bending device and the pressing means is rotated to edgewise bend a predetermined portion of the flat wire. Then, the flat wire is fed until another portion for the next edgewise bending comes to a predetermined place and the same operation is repeated. By repetition of such operation, a coil made of the flat wire by edgewise bending is thus produced.